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How much thrust is produced on an A320 at takeoff and during cruise?
Where can you get the drag polar of the A320 at cruise and TakeOff?

To have an idea of thrust you can check engine public data   (Maximal thrust is usually during T/O)

resource location is off topic as defined by the help center. You'd better directly ask for the polar instead of its location.

Are you asking for the thrust or are you asking for the drag polar? Those are two different questions....

A320 family's engine of choice is the CFM56-5B. Now there are multiple variants of this engine. But on average the takeoff thrust for the models -5B1/B2 and -5B3 are between 30,000 to 33,000 lbf.
Other variants have a lower thrust rating between 21,000 - 24,000 lbf and 27,000 lbf.
The cruise thrust is lower of course since the aircraft has already taken off and now in upper atmosphere, with low drag and running at its best efficiency. Cruise thrust is about 4,700 to 5,800 lbf, although these are the maximum rated cruise thrust, so the engine thrust is always lower than that.
Say if the engine is rated for 5,800 lbs the actual thrust would be roughly about 5,300 - 5,500 lbs, maybe even lower.
Feel free to correct me if I'm wrong!
Reference
Cfm technical data

Takeoff thrust depends on many factors and needs to be calculated carefully. You can take the max values from the manufacturer in orther to have an idea.
Cruise can be calculated roughly. Let's see an example. We know that during cruise phase all four forces are level.
Lift = Weight and Thrust = Drag
We also know that an airliner such as the A320 is very efficient and can easily have a glide ratio of 18:1 This is known as Lift / Drag (L / D) ratio.
If the plane flies near its optimal L / D of 18 at cruise then the CD / CL is 0.055556. The airplane begins its cruise phase after the climb, but we can assume that its mass is close to that of the takeoff minus the fuel consumed for the climb. Say our weight is 44 tons.
With these data we see that the drag force is 1/18 of the force generated by the mass of the plane. Weight is mass multiplied by gravitational acceleration: 44,000 x 9.81 = 431,640 N. Therefore, drag would be 431,640 / 18 = 23,980 N in this phase.
Let's assume that at the end of the trip and before the descent, the plane could have burned 1.5 tons of fuel; in that case the drag will be 23,162.5 N.
These calculated values are the total drag (induced and parasitic) of the plane, but in cruising flight it is also the same value as the engine thrust, since T = D. If we change in lbf we have values of 5,391 and 5,207, far from the maximum rated thrust for cruise.


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Does a constant power prop exist? What are the tradeoffs compared to a constant speed prop?
Variable-pitch props allow pilots to adjust the angle of attack of the propeller to change the load on the engine.
The most common implementation of this is a constant speed prop where the prop governor adjusts pitch to maintain the chosen RPM.
From a pilot's perspective, we only really care about two things:

Power output
Fuel economy

Using a constant speed prop, you can't directly set the output power - you set the throttle and prop speed and observe the power output.
Using a constant speed prop, you also can't directly set the fuel flow rate - you set the throttle and prop speed and observe the fuel flow (or look up the POH).
Using a constant power control law instead the pilot could set the desired power and have the prop pitch adjusted automatically to maintain that (or if impossible, fail in a similar way to a constant speed prop going off the governor).
It is also possible to pick the most fuel efficient RPM for a given engine load which means that the two inputs (throttle + prop speed) get reduced to one: desired power.
The benefits I see are:

Reduced workload
Increased efficiency

The drawbacks I see are:

Inability to operate the engine at anything other than best efficiency for a given power - but I don't actually know what use case that would be useful in.
System complexity
Certification cost

Has a constant power control system ever been used in aviation? Are there other drawbacks that I'm missing?

Are you looking for an ECU whose input is directly translated in percentage of available power? or directly in a given power (let's say throttle full forward correspond to 200hp, midcourse to 125hp,...)?

In terms of (combustion) engine performance, rpm matters a lot. This surely partly explains why there are constant speed props. In fact, you generally design your engine to have a maximum power for take-off speed, then maximum efficiency for cruise speed. Also, some unstable phenomena forbid to stay in some areas of the operating range (especially for turboengines).

It isn't clear to me what you are actually hoping to achieve.  For example, your comment that you cannot set fuel flow but can only observe it is incorrect.  You absolutely can set the fuel flow.  Every time you move the throttle the fuel flow changes.  If you want to set a specific fuel flow simply adjust power and prop to a setting that will achieve it.

@ManuH yes, but also factoring in available prop pitches to pick the most efficient way to produce 125hp etc

@MichaelHall Throttle does not set fuel flow (but does affect it) - this is obvious by the fact that changing the prop setting while keeping the throttle constant changes your fuel flow (ie. reducing RPM with a constant throttle will reduce the fuel flow)

@digitalPhonix, What is the difference between setting and affecting?  If you affect it then you can control it, and if you can control it you can set it.  Right?  And I actually said "If you want to set a specific fuel flow simply adjust power and prop to a setting that will achieve it."  So I understand prop affects it too.  The point is, fuel flow is just one performance metric, one that can be set with existing controls.  So again, I am not sure what you are asking, or what problem you are trying to resolve...

The prop lever directly controls the prop speed - once you set the prop speed no matter what you do with any other controls (withing the prop governor's ability) the prop speed will stay the same; you set the prop speed. This is not the same relationship between throttle and fuel consumption; you affect the fuel consumption by both prop speed and fuel consumption.

You affect the fuel consumption by prop speed and throttle (and mixture, altitude etc.)*

2 points: Firstly, "From a pilot's perspective, we only really care about two things: power output [and] fuel economy." While fuel economy is an issue, what pilots want from the engine is to maintain the desired speed (vertically and horizontally), and the specific power value is of no interest (even when you need maximum power, you are not aiming for a specific value; you want the closest you can get to what would give the rate of climb and airspeed or acceleration that you would prefer in the situation.) ...

Secondly, no specifically propeller control mechanism would have full authority over power. What you are asking for seems to be a single-lever engine management system that optimizes the propeller pitch automatically.

@sdenham A) no - as a pilot I care about more than speed; that's the whole reason I have the ability ways to achieve the same speed B) correct - in the same way the prop control doesn't have full authority over prop speed but does have the correct authority when operating within some envelope.

@digitalPhonix Of course we care about more than speed, but saying that is just a way to dodge the issue here, which is that power is not one of those other things we care about for its own sake.

@sdenham - ok, is your statement that prop RPM is something a pilot cares about for its own sake? I don't understand the point that you're making

@digitalPhonix You have a point, and I will even spot you this one: power (WRT the nominal max) is the parameter used for less-than-full-power takeoffs in transport aircraft. This does not help, however, in making the case for a specifically const-power propeller being a better alternative to a constant-speed one, particularly given the complications of implementing the former. Given an airplane with a CS prop, and RPM  and manifold pressure gauges,  is there any situation where you have to be frequently adjusting the engine controls with the purpose of maintaining a constant power output?

There are some aircraft that indeed have just power lever and set the RPM on schedule, e.g. the Pilatus PC-7, PC-9, PC-21 line of trainers. Since they are primarily designed for training future jet pilots, and jet aircraft only have power levers, it makes sense to skip the complexity of separate propeller and condition controls.
However normally there are some cases where you do want to set other than most efficient RPM for current power and true airspeed:

The most common is descent and approach. These are flown with high RPM because

the engine is already spinning fast, so it does not have to spool up if you need to add power to go around and
with retarded power it produces more drag, allowing to expedite the descent when needed (the Pilatus PC-7/9/21 have a ventral speed brake; most turboprops don't).

Failure modes, though for most a feather switch would probably be sufficient.

Do you know how those aircraft measure the shaft power and adjust throttle/pitch to maintain it?

And thanks for those two cases!

@digitalPhonix, I don't know, but I don't think they'd actually measure power, just have the power settings mapped to fuel flow and RPM (it is a turbine engine, so no mixture to fiddle with).

A constant-speed prop lets the pilot select the speed setpoint for the prop/engine system with the prop control. With that control in the full-forward (fine pitch) position, full throttle applied to the engine will result in the engine revving up to its maximum rated RPM.
Then adding pitch to the prop so as to load down the engine (at full throttle) will cause it to slow down to any desired RPM setpoint. At that RPM setpoint, pulling back the throttle will cause the pitch to decrease as the governor system strives to maintain the RPM setpoint.
Working the throttle and the prop controls in this way lets the pilot select any possible combination of prop pitch and engine RPM desired. The operation manual contains charts that specify the power output of the engine for every possible combination of those parameters, and on those charts the "best power" and "best economy" combinations will be marked.
So, if the pilot has to execute a climb during cruise, they will select the "best power" combination of manifold pressure and RPM for that altitude by adjusting the throttle and prop controls necessary to produce it- and then monitor the resulting cylinder head and oil temps to make sure they don't go into the red. Once they arrive at the assigned altitude, then they will go back to the "best economy" setting for that (new) altitude.

Why would a pilot ever want any setting that isn't best economy for a given power setting? Eg. In a C177 I can produce ~125bhp @ 2000ft using: 2100rpm/24" (burning 9.0 gph), 2200rpm/23" (burning 8.9 gph), 2300rpm/22.5" (burning 8.7 gph), 2400rpm/22" (burning 9.0 gph) and 2500rpm/21.5" (burning 9.2 gph). Why would I ever pick anything other than 2300rpm/22.5" if I wanted to produce 125bhp?

And yes, I understand it allows you to select any possible operating point - I'm asking why are the inputs speed and throttle? Power and throttle would also allow you to pick any operating point; as would power and rpm. (The second part of the question was asking about dropping the second input, in which case you can't select any operating point)

there's no way to measure power directly; you need to put RPM and manifold pressure onto a chart from which you then read off the resulting horsepower.

@nielsnielsen, that most GA aircraft don't have a power indicator installed does not mean there is no way to measure it. Larger piston airliners usually had one (often labelled BMEP) and it was used as a reference to set mixture for best power. These days turboprops usually only have torque and RPM though.

I know in maritime applications too the shaft power is directly measured so the measurement part is a solved problem (maybe not within the weight/cost constraints of GA - in which case that would be the answer to my question).

Light planes can also adjust the mixture - this is often used to help with engine cooling too. I do that in my Cardinal as well.

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What is the threshold between high Aspect Ratios and low Aspect Ratios?
Oftentimes when describing flying organisms and vehicles, their wings are said to have a "high aspect ratio" or a "low aspect ratio". Sometimes the papers (that I read) gave the numbers, but more often, they would just leave the explanation at that.
So I was wondering, in general, what is the minimum ratio that would make it a "high AR" and what is the minimum ratio that would make it a "low AR"? Is there a threshold to be met, or is this analysis of AR rather relative and or subjective?

The boundary depends on the type of aircraft. Fighter wings will be called high aspect ratio when the same aspect ratio in a glider wing will still be called low.
Generally, values below 5 are low, regardless of aircraft type.
With passenger aircraft, the boundary might be around 8.
Gliders will only have a high aspect ratio if it surpasses 20.
Still, there is no defined boundary and in the end the choice depends on the whims of the author.

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What is Circulation in aerodynamics?
Can someone please explain the concept of circulation? I am able to understand the mathematical form i.e. it is the line integral of the velocity field. But I am not able to understand the physical meaning of circulation.

It has been explained to me that this concept of circulation is purely a mathematical concept.  But, I look forward to some clarification on this because diagrams showing forward flow on the bottom surface of the wing don't lend themselves to aiding understanding of actual flight.

You may read how it flies? which is an excellent resource to understand basics about aerodynamic of an aircraft.

@Gerry, that's the one I was thinking about, thanks!

Do the answers in the other question resolve your understanding? Or do you need further clarification?

@Gerry I think this question could be considered a duplicate of the one you linked to. I thought Pilothead's answer was a pretty good description of the concept in terms a layperson would understand.

Circulation does not mean that any fluid particular is traveling in a circuit around the airfoil. One way to look at circulation is that it's a description of how much a uniform flow has been turned asymmetrically by the body.
Another, slightly more technical way, is to consider the flow around a rotating cylinder (which produces lift) as a combinatory sum of a uniform flow (free-stream flow), a doublet flow (non-lifting) and a vortex flow (which produces circulation). See this illustration excerpt from Anderson, Fundamentals of Aerodynamics.

Therefore, circulation can be regarded as the path of the fluid when the symmetrical components have been taken out, which is indeed circuitous.

I found this truly ancient video quite helpful when I was trying to comprehend the concept of circulation.
Now, I have no idea whether my intepretation is righ, but I would describe the circulation as the motion particles of air in the path of an airfoil make as the airfoil passes by them.
This effect can be seen in the last 30 seconds of the video.
The trick is to change coordinate system: Instead of looking at the flow of air from the perspective of an airfoil, you should look at the flow of the airfoil from the perspective of the particles of air.

The video shows an airfoil shedding vortices, but that has little to do with the main question, that might be stated as follows: Does a speck of dust caught in the midst of that 'circulation', really revolves round the wing...? or is the Kutta-Joukowski circulation just a useful mathematical construction...?

I don't think that the Kutta-Joukowski circulation model is useful or practical.  It seems like an abstraction to me.

Yes, the airfoil does shed vortices as it starts to move and as it stop in the end of the video, but what I was referring to, was the movement of a particle as the airfoil passes by it, forcing it to move. This movement is, if not completely, then very close to circular.

@MichaelHall All the important analytical results in aerodynamics is derived from Kutta-Joukowski...I don't know why you would say it's "impractical"

@Jpe61 - I don't see any point at which particles circulate forward along the lower edge of an airfoil that is moving through the airmass.

@Jimmy - I am not saying it might not be useful as a mathematical abstraction to enhance understanding of advanced engineering concepts, I am saying it is not practical in explaining basic principles of flight to a non-engineer.  I am not an engineer, but I graduated first in my class in Navy Pre-flight training so I had (at one point) sufficient knowledge of aerodynamics to fly and teach others.  This concept does nothing to clarify my understanding of how an airplane performs and responds to pilot inputs.

@Michael Hall correct, none do, but as the particles have slided down the top of the wing, they are accelerated at the direction of the movement of the wing, and downwards, making their path somewhat circular.

I am disappointed to see that this thread petered out. You were getting to the nub of the crazy theory that circulation (the path integral of the velocity vector ) is the source of lift, as described by Lanchester, Prandtl and more recently, Marchaj. Come on guys, muscle up and help me burst this crazy bubble!

@alan.raceQs well, this subject is waaaaay beyond the comfort and competence zones of 99.999% of ppl. Pilots are just happy that something, be it circulation or Bernouilli keeps them up in the air, while scientists are dickfencing about the CCC explanation of lift


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How to use Rudder during takeoff in single engine propeller aircraft? e.g. Cessna 172
Background: I am a complete beginner on Flight Simulator X: Steam edition, using a simulator setup with rudder pedals with realism set to the max (to simulate more realistic flying).
I understand that rudder use is essential to align the aircraft to the runway centreline during takeoff due to the left turning tendencies. However, I cannot seem to consistently align the aircraft to the runway centreline during takeoff. Sometimes, I just run parallel to the centreline.
Questions:

Is this common in real life flying? Are actual pilots consistently able to align the nose wheel to the runway centreline during takeoff in such single engine propeller plane or am I being too idealistic?
How is the operation of rudders in an actual aircraft like? Slow smooth gentle depression e.g. to the right pedal each time the aircraft swerve to the left or are the left and right legs constantly moving in quick succession to keep the aircraft aligned to the runway centreline?
Generally, how much of a push is required on the pedals during takeoff? It seems to be very very slight 1cm touches to my rudder pedal on the simulator. Is that realistic?

Thanks so much everyone! All answers are appreciated!

I've got a few hundred hours in spamcans, alignment with the runway is not problem, but I cannot get FSX to behave correctly on takeoff, rudder pedals or not!

Related: How much rudder input does a Cessna 172 require during the take off roll?

As with so much else, using the rudder to stay centered is not something you think about, at least after the first couple of times.  It's like riding a bike: you just do it, reacting to the feel of the aircraft.  Which IMHO is why PC flight simulators aren't all that much use for training: there's no force feedback.  (Though admittedly I learned to fly before I even owned a PC.)

Is this common in real life flying? Are actual pilots consistently
  able to align the nose wheel to the runway centreline during takeoff
  in such single engine propeller plane or am I being too idealistic?

In my experience flying primarily light singles its not terribly difficult to stay aligned on the centerline during takeoff. Even my first solo was nicely centerline. However the more powerful the aircraft the more the tendency and the more control/care may be required.

How is the operation of rudders in an actual aircraft like? Slow
  smooth gentle depression e.g. to the right pedal each time the
  aircraft swerve to the left or are the left and right legs constantly
  moving in quick succession to keep the aircraft aligned to the runway
  centreline?

All control inputs should be smooth and with care. I generally ease onto the right pedal as I apply throttle and ease off/back on to stay center line.

Generally, how much of a push is required on the pedals during
  takeoff? It seems to be very very slight 1cm touches to my rudder
  pedal on the simulator. Is that realistic?

This is what most home sims are worst at. Real light aircraft rudder pedals take a fair bit of force to work an have far more than a 1cm throw. I would add a curve to your response so that the initial throw of the pedals is less sensitive.

Thanks so much for your very detailed response!

In actual practice you will find it easier to quickly perceive any deviation (drifting) toward the left or right edge of the runway if you positon the aircraft so that the runway centerline goes right under your seat.  So that you are essentially "sitting on" the centerline.  This makes the runway centerline appear to project perfectly forward in your vision, issueing out from behind the instrument panel from a point directly above the center of your control yoke, without "leaning" left or right.  Any slight "lean" in the centerline to either side means you have drifted slight left or right of this ideal position.  (A photo or illustration would really help here.)  You'll be to see this immediately, and make a correction to come back to your original position, as far as left/ right drift goes.
In an airplane with side-by-side seating, this method does not put the nosewheel exactly on the centerline, but that's ok.  There's rarely any reason to put the nosewheel exactly on the centerline, and this method allows you to perceive any lateral drift sooner than if the nosewheel were on the centerline, because of the way it allows the centerline to project perfectly straight forward in your visual field as long as you are maintaining the target picture.
It's like the difference between sighting a gun by holding it directly in front of you, versus sighting a gun by holding it several feet off to one side of you.  The latter is analogous to the sight picture you get in a side-by side airplane when trying to take-off or land with the nosewheel, rather than the center of your own seat, aligned with the runway centerline.  Unless the runway is incredibly narrow, the tradeoff in terms of increased obstacle clearance at the wingtips is not worth the greater difficulty in recognizing that you are drifting further to one side or the other, or that you are not actually aimed perfectly parallel to the runway heading.  Both of those things are bad for the landing gear, whereas having the nosewheel two feet to one side is not bad for the landing gear.
To get a hands-on feel for how useful the effect I'm talking about is, sometime when you are driving down a long straight road with no other cars around, move your car over so you are driving with the highway centerline passing right under your seat-- as if you are "straddling" the centerline between your legs.  If the road is very long and straight, you'll get the sight picture I'm describing here, and any slight deviation from this position will be immediately apparently.  It will be much easier to maintain this position very precisely to a tolerance of just a few inches, than it is in the usual driving position.
At the very least, don't move on to try landing or taking off with the nosewheel right on the centerline, until you have completely mastered the simpler method described in this answer.
Try this:  while taxiing down a long straight taxiway, position the aircraft so that the taxiway centerline goes right under your seat and projects forward in a perfectly straight line, and make sure you are sitting up perfectly straight, directly behind the middle of the control yoke, and memorize the exact point on the front of the cowl where the centerline disappears from view behind the cowl.  That's your "sweet spot" or "gunsight point" -- remember it for later.  (It's much closer to the edge of the cowling-- much further from the center of the cowling-- than you may expect.)  When you are lining up on final approach, you can determine whether the aircraft is left or right of the runway centerline by looking at whether the runway centerline is "leaning" slightly to either side,  and you can detect any left or right "drift" by looking for the first slight hint of any "lean" starting to develop in the appearance of the runway centerline, and you can tell whether the aircraft heading is exactly the same as the runway heading by seeing that the (non-leaning) runway centerline disappears behind the cowl exactly at the "gunsight" point described above, and not at some other spot a few inches off to either side.  Note that you must actually be in motion on the taxiway when you pick the "sweet spot" or "gunsight point".  Otherwise, even if the runway centerline is passing directly under your seat, the aircraft could be pointed a few degrees off from the actual runway heading, and it might be hard for you to detect that.  When you are in motion, it is obvious-- if the wheels are firmly on the ground, and the centerline is staying under your seat, then the aircraft must be pointing exactly parallel to the taxiway centerline.
Naturally, on final approach, this cowling "gunsight" tip only applies when there is no crosswind or when you using the wing-down method rather than the crabbing method to correct for crosswind.  If you are crabbing, the centerline will disappear under the cowling at some other point. But looking for the appearance of any "lean" in the runway centerline always will tell you whether you are on the centerline or not, and as long as you are trying to land with your seat rather than the nosewheel on the centerline, it will work just as well during the actual flare and touchdown as it worked when you were still a mile away on final approach.
PS-- if you a pilot with left-seat experience just learning to fly from the right seat, and you find yourself tending to land with the nose cocked off to the left, pay attention to the "gunsight spot" on the cowling the next time you are taxiing down a long straight taxiway (or while you are in motion on the runway).  You may that your landings suddenly improve.

Maybe the question was more about rudder "feel" and avoiding overcontrolling-- still, hope this helps a little.

Some animated illustrations or actual video would really help this answer.  Some of these things are hard to explain in words but easy to see with your eyes.

It is very rare to take off in perfectly calm conditions (wind can add or subtract from "left turning forces").  Rudder inputs are added on a "as needed" basis by the pilot, usually in small increments.  Taking an hour at a local airport in a 172 may be your best answer.
Keep in mind, with side by side seating, your eyes are slightly off the centerline when the nose of the plane is on it.  The important thing is to have throttle and rudder working together.  Smoothly add throttle, don't just jam it. You need to accelerate to rotation speed (around 55 knots), controlling your line with the rudder.  The center line is your reference, it does not have to be perfect, just as straight as you can until lift-off.
A few tries with an instructor should be sufficient to compare with your simulator.

I cannot talk about the realism in flight simulator these days, I haven't used it since I became a pilot many years ago. From my experience back then I found that ground handling was one of the least realistic aspects of the experience compared to the real thing, so I wouldn't worry too much about that aspect.
Keeping on centerline is a matter of experience, you learn to anticipate how much rudder you need. I can't even tell you how much I push because I don't even think about it, it's natural. I don't make full-deflection inputs on the rudder on takeoff, and I may be constantly adjusting my input depending on conditions. I have no problem keeping it on the centerline, although in training it's very common to make mistakes.

Thanks so much for your input! I am hoping to gain some basics through sim before the real thing. I guess I have to manage my expectations.

Teaching yourself to fly in flight simulator isn't really good preparation for the real thing IMO, if you want to learn to fly just go for it.

I will be starting flight school in a few months, just thought it will be beneficial to do something to prepare myself. Thanks so much!

@Flightsimrightnow Consider doing a "discovery flight" now; they're short but usually much cheaper than a regular lesson. Some things you just have to feel to understand, and it will show you how accurate your sim is. You don't want to learn the wrong things now and have to unlearn them later.


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XFoil aglorithm for generating a NACA 4-digits airfoil
I need to generate NACA 4-digits airfoil points in the exact same way that XFoil software does, I need the algorithm so that I can convert it to another programming language,other than fortran...
I have looked into the source code of XFoil and found the file called "naca.f".
It does generate the airfoil, and it works fine, but it is not the same as when using the software and typing:
>> naca 2412
>> ppar n 150
>> psav naca2412.dat

The points are -simply- not the same
and the problem is that, when I apply a source-vortex panels method (implemented by me) on both the two different airfoil data, the results are within a 2% change for lift, and about 12% for moment, (for the same panels method code), which is quite unacceptably large.
So I really need to know how does XFoil exactly generate/modify the airfoil data after the subroutine "NACA4" is called.

Not sure that questions about the algorithms of a particular software package is on-topic here, even when the software itself is about aviation.

@RalphJ You aren't wrong, but once again, unfortunately there isn't an Aerospace Engineering SE and we're left to the gracious hosting of Aviation SE.

@RalphJ I know aviation is not necessarily aeronautics engineering, but I don't know any other space for that.

Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on [meta], or in [chat]. Comments continuing discussion may be removed.

Not every question that can be asked will necessarily belong anywhere on Stack Exchange. That doesn't mean that the question itself is necessarily a bad question per se, just that it may not fit the SE model. Even with Aviation.SE being the closest thing actually available to a hypothetical AerospaceEngineering.SE, that doesn't mean that everything that might fit into the hypothetical latter, meets the criteria for the former. The fact that this question is being 'answered' as a back & forth, rather than with the answer to the question suggests "not a good fit for this format."


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Are UDF/Propfan Engines Thrust Producing or Power Producing?
For the purposes of aircraft performance (best endurance/range speeds, Vx, Vy, etc.) would a propfan be considered a power producing engine or a thrust producing engine?
I would imagine it would be power producing (with some exhaust thrust like a TP400), since they are closer to a turboprop than a turbofan. However, these engines always seem to be rated in thrust rather than power. I always thought that was more of a marketing gimmick, since manufacturers want these to compete with turbofans, but I haven't been able to lock down a concrete answer.

These answers should help.

Both. "Power producing" and "thrust producing" are only approximations. That said, propfans are improved turboprops.

The original definition of power by Watt was derived from a horse turning a mill wheel (against its friction).  Clearly P = W/t = F × d/t.  The depiction here is actually showing linear force or thrust.  One might even imagine the force increasing the height of the object as excess thrust.  The mill wheel description is in the same article, along with the math, under "History".

I happen to have an engine deck representative of a GE-36.  It is tabulated in terms of thrust, so I'll have to do some manipulations to get a power curve to compare with.
Here is a chart showing full throttle thrust lapse (vs. Mach) for a GE-36 propfan at 35,000 ft.  I've multiplied thrust lapse by Mach to give something related to power.

From this, it is clear that neither is constant with Mach.  So it doesn't behave as a classical thrust producer or power producer.
I divided the fuel flow by each of those curves to result in something proportional to TSFC and to SFC.

I'm not specifically sure what is happening below Mach 0.3.  Often specific fuel consumption shows behavior like that -- but usually when thrust or power go negative or close to zero (not happening here).  In general, it is much better to interpolate in fuel flow rather than SFC exactly because of stuff like this.
So lets just ignore everything under Mach 0.5 -- we are at 35,000 ft and full throttle after all.  (It might actually be better for me to pull back the throttle a bit, but I'm not going to spend that much time on this).
Above Mach 0.5, the PSFC curve is surprisingly flat.  It would seem reasonable to treat the engine as power producing.
Long answer -- behavior of actual engines is much more complex than 'thrust producing' and 'power producing' idealizations.  You should work to build an engine deck that models off design performance for the engine cycles you're considering -- this means variation with airspeed, altitude, and throttle (at least).
No, I won't give you the GE-36 deck I have.

Interesting;
It seems to always be taught (at least at a basic level) that best endurance for a piston engine is speed for minimum power required, and that best endurance for a jet is minimum thrust required (L/Dmax). This goes off of the assumption that less power = less fuel consumption for piston engines, and less thrust = less fuel consumption for jet engines.
I guess the crux of my question was whether an aircraft with this engine would experience best endurance at min power required, min thrust required, or somewhere in between.

You're working with the idea that these rules are based on less power=less fuel or less thrust=less fuel.  Both are always true.  These simplified rules are actually derived from the slightly more complex idea that fuel consumption is proportional to power (PSFC) or fuel consumption is proportional to thrust (TSFC) -- and that the constant of proportionality is independent of airspeed (and throttle).  We can calculate both fuel consumption metric, so we're interested in which is most constant with airspeed.  Blue line, second chart.

Thrust is a Force and Power is Force × Velocity.
Let's look at the application of those terms with respect to propulsion.
All aircraft are moved by thrust force.

why do we even talk about "power"?

It seems to make sense when the units of Power as Force × Velocity are rearranged to:

Power = Force × distance/time

Now we can say Power = Torque/time
Anything with a rotating mechanical output is most aptly described in this manner.  The torque turns the wheel, the wheel transfers the thrust to the ground.  Thrust is measured by:
(Torque/wheel radius)/time = propulsive Force/time
So why don't we say Thrust/time?
It seems this is a more proper comparative definition to Power output.
In reality this is what all engines generate.
In aviation, Torque turns propellers against their drag.  The prop airfoil produces thrust (thrust/time).
A jet produces thrust without creating rotational motion, or does it?

a jet engine must create "power" to turn its compressor.
a fan jet must create "power" to turn its fan

So, power is Torque/time.  Thrust is (more correctly) Force/time.
In all applications involving Power, the distance term will cancel out leaving thrust.


text:
ILS Frequency Assignment In Dual Nav Radio Setup
With a dual Nav radio setup (On autopilot panel) does the ILS frequency of the runway you're about touch down on need to be entered into both radios or just one? Cheers.

It doesn't need to be entered in either receiver.
If you want the ILS info displayed on the #1 display, enter it in the #1 nav radio. If you want it on the #2  display, enter it in the #2 nav radio. If you want it displayed on both, then enter it in both. If you don't need it displayed - perhaps you're flying a visual approach - then you don't need to enter it anywhere.
Some procedures may require a particular setup, but in the general case it's up to the pilot.

Thanks for taking the time to answer as it's confirmed what I understood to be the case. A certain flight simulator states that the RWY ILS frequency needs to be entered into both NAV 1 & NAV 2 radios when flying an ILS/DME approach. I realise of course that the sim world and real world  don't always correspond exactly with each other @Ralph J


text:
Is there any top document for ATC glossary?
I have been searching for some official documents that have all ATC phrases, because I wanted to refresh some of the phrases for ATC, but I was not able to find any other than:

Eurocontrol Phraseology database (https://contentzone.eurocontrol.int/phraseology/Default.aspx)
FAA pilot controller glossary (https://www.faa.gov/air_traffic/publications/media/pcg_change_1_dtd_12-2-21.pdf)
Glossary from the faculty of transportation sciences CTU Prague (https://aim.rlp.cz/predpisy/predpisy/dokumenty/L/L-Frazeologie/data/effective/cast_II.pdf)

Is there any official document produced by any international organisation (for example ICAO) that almost every country respects or do my search results have everything needed for standart ATC communication?

Add this for your US list: https://www.faa.gov/regulations_policies/orders_notices/index.cfm/go/document.information/documentid/1029467

International standards of phraseology are laid down in ICAO Annex 10 Volume II Chapter 5, ICAO Doc 4444 Chapter 12 and in ICAO Doc 9432 - Manual of Radiotelephony and in  Amendment 4 to the Acceptable Means of Compliance and Guidance Material to Regulation (EU) No 923/2012. Many national authorities also publish radiotelephony manuals which amplify ICAO provisions, and in some cases modify them to suit local conditions.

Source


text:
Are winglets symmetric airfoils? (Cessna Citation M2)
I want to simulate the Cessna citation M2 in XFLR as a student homework assignment. This aircraft has a NASA high-speed 0213 airfoil (which is not symmetric) and a winglet, which can be seen in the picture below.  Is the airfoil of the winglet the same as the main wing or a symmetric one is used?
*If you do not know for the Cessna M2 specifically, what is the common practice?

It is not unreasonable to continue into the winglet with the wing tip airfoil. In order to work best, the circulation (local lift coefficient times local chord) at the root of the winglet should continue with the same value as on the wingtip. A steep gradient in the circulation distribution would increase induced drag.
Since a change in the angle of attack will mainly affect the wing circulation, the winglet incidence and airfoil must be matched to the desired working point of the wing. This can both be done by cambering the winglet airfoil and by selecting the proper winglet incidence.
Note that a high lift coeffcient at the wingtip needs to be bought with a steeper pressure gradient in the pressure recovery zone. If you now add the same gradient at the winglet root, flow separation in the corner between wingtip and winglet will be hard to avoid. This will show up as a drag increase and is normally counted as interference drag. Make sure that the pressure gradients at the operating point are still shallow enough to avoid separation.

This is what blended winglets seek to avoid no?

@JohnK Yes, they make more room for the intersection and reduce the risk of flow separation in the corner by changing the corner into a bow.

There is no reason to assume that winglets have symmetrical airfoils -- in this case or in general.
Furthermore, the wing is likely twisted, and the winglet likely also has twist that manifests as toe-in or toe-out.
Generally speaking, very few aircraft have sufficient information published in order to perform a high quality aerodynamic analysis.
At the same time, it is great to learn about how sensitive the wing's performance is to these different parameters.  You might try starting with symmetrical winglet airfoils and zero toe-in/out.  Look at the lift distribution and compare to an elliptical distribution.
Then, add some toe-in/out and see what changes.
You should be able to achieve the same effects using either twist or camber of the winglet.  So for simplicity, I would use a symmetrical foil and conduct an early study just changing twist.


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How does a plane land without any radio connections?
It has been reported today that the German government plane "Konrad Adenauer", operated by the Luftwaffe, had a total loss of radio connection and diverted to Köln.
That made me think the following:

It was extremely fortunate that the problem did not occur somewhere over the Atlantic in the middle of the night.
How on Earth did they communicate their intend to land to the airport?

So, assuming it was indeed a complete loss of radio communications, how does a large plane like this indicate it has to land on an airport were it is not scheduled to land? Has that necessarily involved some jetfighters that communicate 'manually' (literally)? Is there an established protocol, e.g., a specific flight pattern?
1 http://www.spiegel.de/politik/deutschland/angela-merkel-verpasst-g20-start-flugabbruch-wegen-komplett-ausfall-des-funksystems-a-1241166.html

The Konrad Adenauer did not have a complete loss of communications, the regular radio comms were down but they did still have a satellite link for voice communication. They diverted to Köln because the pilots feared other systems could be down as well making a landing at Schiphol too risky. source

related: https://aviation.stackexchange.com/questions/3794/how-would-an-airplane-land-if-the-on-board-radio-breaks-down?rq=1


text:
Staying oriented in VFR
This is something I have been questioning more and more often on how pilots do it. So, let's say we are flying on a new location and know very little about it. When flying around and keeping the location of the aerodrome we took off to later return back to it, how do we plan to consider which points to reference and which points represent what when flying?
Might be worth to mention VFR is in practice. Let us assume we do not have a GPS.
As an example where I have been flying I got references like a prison and a stadium that indicates a fly path back to the aerodrome, but I got to know those thanks to my instructor and become more aware of them. But when I think about it, at the start I had no idea. And when I consider way ahead once I have the ability to fly alone, I often think of how will I be able to understand which points references what, how can I quickly understand where I am and what is best for me to try and plan ahead to stay located when in flight.
Apologies if it is really obvious it is still something very recent to me and I have this worry recently. Just though it could be something I could start gain awareness, the sooner the better?
Thank you in advance!

Related: What are good apps to help with VFR navigation on my first solo?

It's something you get better at with practice and time in the air.  Just keep at it.  If no GPS, you can also use VFR radials to make sure you're near the right place/area. And often you can pick out large landmarks for reference also.  Highways, radio towers water ways, etc. Circle them on your sectional/map and make sure to spot them as you go.

Thank you @CrossRoads ! I am slowly pushing myself to become aware of them. Also need to look more at the map prior to next flights and, like you mentioned, try and become aware of it more often. Best practices from the start make up for the later eh? :) It does seem more reliable to go after landmarks like lakes and hills instead of buildings as I am not sure how can I quickly distinguish a building when flying :P

Buildings are tough, unless they are quite large. Natural landmarks are often easier to spot as they are large and can be seen from quite a distance.  For example, in my state we have a huge reservoir that feeds the large city on the coast (and many others as well). Easy to see from miles away, and I know I'm about 50 miles from home when I see it.

Back when I was a boy hanging around airports, there was a saying, "I fly IFRRR." In other words, "I follow roads, railroads, and rivers." When flying with my father over the Iowa (a state in the American midwest) flatlands, if we got disoriented, we knew that all we had to do was look for the water tower every small town had, and on which in big letters was the name of the town. And it was not unheard of to simply land in a farmer's field, walk to the farmhouse, and ask where you were. In the American west, if you could see the mountain peaks, you knew where you were. It was a simpler time.

This is amazing feed back! Many thanks to you all! It comforts me to know is part of the path :)

Many of the features marked on your sectional chart are there precisely because they're things a VFR pilot should be able to see from the air and use as landmarks for navigation using "pilotage".
If you're preparing for a cross-country trip, you start with a straight line from origin to destination than then adjust it slightly so that it passes over these features as checkpoints every 10-15nm, and you'd put each of those points in your nav log as your flight path.  Then you do the additional calculations (wind, time, etc.) to turn that into something you could, if necessary, follow via "dead reckoning".
Even if you don't have GPS, you may have a VOR receiver (or ADF, if in a really old plane) that could be used as well.  DPEs here require that you be able to use VORs to fix your location on a PPL checkride; I don't know if that's everywhere, but IMHO it's a good idea regardless.
If all else fails, or any time you are in immediate danger, you can always call ATC and ask for help.  But until you've had the training on all the above options and demonstrated reasonable competency with them, your instructor shouldn't be allowing you to get yourself into such situations.

No, my instructor is quite great and I am confident he wouldn't allow me to go through such thing if I am not quite prepared :) It is just my mind starting to rumbling on it. Wandering how he does it so easily and wishing to be there! :) But thank you for your answer, all of this is amazing feedback to start being able to focus a little more every day, on this ^^


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Program to make glider polars
I was using flow5 to make some speed polars for a glider with real dimensions, however I read about PGEN (polar generation software) that could simulate the thermal effect, but apparently it is an internal program at a university. I was wondering if you know of any program that is similar to include the bank angle effect, circling radius and making velocity polars for thermals,
Thanks in advance.

I assume you are hoping for a treatment of circling flight that is more sophisiticated than simply increasing the wing loading as a function of the bank angle?


text:
IAS vs ground speed when calculating speed to fly in wind
It's common for discussions around a glider's Polar Curve to describe how to use the Polar Curve to identify the best speed (Indicated Airspeed, IAS) to fly in a given wind condition (let's assume a straight headwind for this discussion). You do this by calculating the tangent to the curve from the point (wind speed, 0) on the graph, and the IAS where the tangent meets the curve is the IAS that will give you the best glide slope for that wind condition.
However, wind is reported relative to ground speed, but IAS is definitely not equivalent to ground speed at higher altitudes. Why is it OK to "subtract" windspeed from IAS on the polar when they aren't comparable really? Is the error just so small that it doesn't matter in practice? If you wanted a mathematically accurate calculation would you first have to convert wind speed to IAS or vice versa (probably by using the 2% per 1000 ft estimate)?

Would you put a picture of the chart in your question please?

You are 100% correct to suggest that if we are working with a polar curve that has units of IAS, the wind speed needs to be converted to similar units before we can properly find the best speed to fly for best glide angle over the ground by means of the tangent line method.
Or conversely we could convert the IAS to TAS, and use the true wind speed.
Usually it doesn't matter much, but sometimes it might.  Especially at high actual altitudes or density altitudes.
You clearly have the understanding sufficient to work out for yourself how much the difference would be in various real-world situations.


text:
Glider Flying Handbook page 5-6 error on effects of weight to stall speed?
I've been reading the FAA's Glider Flying Handbook, 2013 (FAA-H-8083-13A). Page 5-6 in chapter 5 states the following, but it doesn't seem right to me.

The heavy glider has a higher stall speed and a higher minimum
controllable airspeed than an otherwise identical, but lighter,
glider. The stall speed of a glider increases with the square root of
the increase in weight. If the weight of the glider is doubled
(multiplied by 2.0), then the stall speed increases by more than 40
percent (1.41 is the approximate square root of 2; 1.41 times the old
stall speed results in the new stall speed at the heavier weight). For
example, a 540-pound glider has a stalling speed of 40 knots. The
pilot adds 300 pounds of water ballast making the new weight 840
pounds. The new stalling speed is approximately 57 knots (square root
of √ 300 + 40 = 57).

Increase of stall speed is not proportional to the square root of the raw increase in weight, it's proportional to the square root of the percentage change in weight. So in this case, the new stall speed would be
= StallSpeed * sqrt(NewWeight / OriginalWeight)
= 40 * sqrt(840/540)
= ~49.9

Another way to see this is incorrect is to do what the example says at first and double the weight (540 * 2 = 1080), which should increase the stall speed by 40% to 56.4 knots. So surely only increasing the weight by 300 pounds doesn't have the same effect. And by the math at the end of the paragraph, sqrt(540) + 40 = 63.2 knots which is clearly not equal to 56.4 knots.
Am I correct in my thinking here, and there is an error in the handbook?

You are correct.
The handbook is correct in the earlier example -- double the weight, stall speed increases by $\sqrt{2}$.
You are correct in the final example.


text:
Does Best L/D sink rate increase as altitude increases?
As a glider pilot, we learn that Best L/D airspeed does not change with altitude. That is, the Indicated Airspeed (IAS) to fly in order to achieve Best L/D is the same no matter the altitude or air density. Additionally, that Best L/D does not change either.
Best L/D is calculated from the polar curve, which calls out a specific sink rate for that IAS. However, this sink rate only applies to standard atmospheric conditions, right? Since True Airspeed (TAS) increases with altitude (and thus ground speed, assuming no wind), in order for the same L/D to be achieved must sink rate also increase proportionally? Many discussions on glide performance discuss sink/lift/wind and speed-to-fly (i.e. MacCready), but seem to omit this detail which seems important to understand. Am I thinking about this correctly?

Yes you are.  The indicated airspeed and glide slope change little with altitude (until critical Mach number becomes a factor), but true airspeed does change.
Drawing the triangle of sink to horizontal distance gained, the hypotenuse is the glide slope.  At a higher TAS, the ratio holds, therefore the sink rate and horizontal distance gained rate both increase.

Yes, the indicated airspeed for best sink will be constant with altitude.
The true airspeed for best sink will increase with altitude.
Best sink happens at a particular $L/D$ (not best $L/D$, but a specific value for a given aircraft).  If you think of that $L/D$ as the glide ratio -- or glide slope, it corresponds to an angle for the glide $\theta=\mathrm{atan}(L/D)$.  You can think of this as a glide triangle -- it can be interpreted in either length (altitude, downrange) or speed (vertical and horizontal).
The hypotenuse of this airspeed triangle is the indicated airspeed for best sink -- it is constant with altitude.  Framed as a true airspeed, it increases with the $\sqrt{\rho/\rho_0}$.
The vertical velocity behaves the same way (it is proportional to the square root of the density ratio).
Of course, a VSI (rate of static pressure change) does not operate in a similar manner to an airspeed indicator (pitot probe measuring dynamic pressure).  So when we say 'indicated airspeed', the indicated does not have the same meaning for vertical airspeed.
The VSI suffers from lag and its own calibration issues.  Suffice to say that when we talk about 'true' vertical speed, we're talking about what you would measure with a GPS on a day without thermals or other updrafts.


text:
Is an additional rotor useful on a coaxial rotor configuration?
I can understand coaxial rotors cancelling the need for a tail rotor, however, I am curious as to if the second rotor is needed to actually maintain the same pitch or could be just used to offload the primary disk in a powered auto-rotate capacity?  That would just create more drag I assume.

You could use the second rotor to provide anti-torque function only, as Arthur Young did when developing his helicopter test models at Bell during WW2.  In that case the upper rotor did all the lifting and the lower one had blades that were at 90 degrees and just made drag to generate a cancelling torque.
But that is really inefficient, and Young quickly moved on to using an anti-torque tail rotor (with a decently long arm to minimize the thrust it had to make), not wanting to go the whole-hog coaxial route, with all its mechanical complexity.
So if you want to have a coax machine to do away with a tail rotor, you might as well design it so both rotors are lifting (to realize the efficiency you are seeking by going with co-ax in the first place) and you can easily get yaw control by using a mixing system operated by the anti-torque pedals that adds collective pitch to one rotor and decreases collective pitch to the other rotor equally, in a way that the total lift is unchanged but a yawing torque can be created and varied.  And there you go.

Thank you for this lead, I can see this.... So coaxial with collective on both... Gain altitude and engage a lateral drive to a point of speed allowing auto-rotation and disengaging rotor power...... Autogyro may live after all :)

Well they all glide fine when you take the power off because you pitch the blades down so they can glide forward.  An auto-rotating rotor is just like two gliders that pass each other going opposite directions and lock wingtips so they are forced to glide in a little circle.  One rotor, two rotors going coaxially, or two rotors in tandem, it's all the same.

Yep, however, autogyro going VTOL is what I am after..... No rocket tips or Carter "Jumps"..... Once vertical and moving lateral disengage power and fly lateral at speed then re- engage to go vertical again to land... We got this!

Electric is the key and batteries suck

Hydrogen fuel cells are the key though :)

Just can't make 103 no matter what I do

@Skyhawg I'll nudge you one step further: hydrogen storage is the bottleneck, because the tanks are so heavy. There have been several good tech demonstrators in the past decades, but they all were weighted down (literally) by the terrible energy density once you add the H2 tank into the calculation.


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What was this helicopter photographed on a Chinese aircraft carrier?
I've read this twit
Chinese carrier got photographed by a satellite.

On the nose you can find a helicopter and several people around it.
What helicopter is that?

The noise is strong enough to obscure any details smaller than "it lacks wings."

Can't say for sure, but the size and shape (as far as can be determined from the picture) seems to match the Aerospatiale Super Frelon, which is built under license in China and is in use with the Chinese navy for shipboard operations under designation Z-8.
The image is of poor enough quality that a more precise determination isn't feasible, but the size and shape match the type and the type is in Chinese service (unlike similarly sized helicopters).

It's really hard to tell from this photo but an August 2019 photo shows a Changhe Z-18 for a similar sea trial.
Wikipedia indicates PLAN Shandong only carries Z-18 and Z-9 but in this picture it seems too big to be a Z-9.


text:
How to use a set of Pressure Transducer to mimic pitot static tube for VTOL vertical airspeed indicator?
May i know if i have 3 pressure transducer, 1 facing upwards and the other downwards to measure the vertical velocity of a VTOL (Vertical Takeoff and Landing aircraft) and another 1 on the nose of the aircraft, do i still need a pressure transducer to mimic a Static port to measure the climb rate? Since i already have 2 pointing upwards and downwards. For your kind advise, thanks!

Unless it's a rocket there's really not enough vertical air speed to make meaningful measurements. All you are measuring is just wind noise. You have much better results using a accelerometer or a radar

You won't be measuring any static pressures because facing the transducers into the sense direction produces dynamic positive pressure which is not subject to temperature compensation or air density corrections at altitude. A Vertical Speed Indicator works by taking static pressure and a calibrated leak inside the instrument to show your climb rate. You can't replicate this using the system you describe.
Even using your suggestion of adding another transducer for static is not enough. You need a rate of change which, as stated above, is normally provided by a calibrated leak inside the VSI.
If you want to explore further options of measuring position in 3d space that don't involve pressure transducers, I suggest looking at gyros and accelerometers.


text:
what are the Common roll angle and roll rate limits for civil flights?
I'm currently doing simulations for eVTOL type of vehicles and for the purpose of controlling the attitude, I'd like to know the common limits for roll and roll rates (more important) that are in place for civil flights. I'm interested both for airplanes and helicopters even though I do prefer information for rotary vehicles.
I've spent a few hours already searching through the web but for some reason, I'm not able to find literal values in documents such as ICAO annexes etc.
So it would be really helpful for me to know at least the approximate values. I appreciate any answer in advance. Thanks
UPDATE with respect to comments:
I am interested in upper boundary, i.e. what rate should not the vehicle exceed. I imagine that there is some at least recommendation that aircraft of a particular type should not exceed this rate, otherwise the passengers can spill their coffee, get sick etc. So it could be also partially dependent on the current wind situation, gusts and so on.
In terms of particular regulatory office, it doesn't really matter as this information should just give some overview of possible values because right now I really dont have any clue.

Are you looking for lower or upper limits (e.g. the aircraft must be able to achieve a roll (rate) of at least XXX, or the aircraft shall not have are roll (rate) exceeding YYY)?

This question is really broad. Aerobatic aircraft are civil one, and they clearly don't have the same limits as an AN-225 fully loaded or a jet airliner full of passengers.

The minimum roll rate is documented in 14 CFR 23.157 (pre Amdt 64), which is used as an accepted means of compliance for the current 14 CFR 23.2135.
As far as I know, there is no regulatory requirement on maximum roll rate. For large transport aircraft, the design target at maximum roll authority is typically around 20 deg/s to 30 deg/s. For example, A320 has a roll rate limit of 15 deg/s at maximum lateral input in Normal Law, while A220 has a roll rate limit of 20 deg/s in Normal Mode.
There is no regulatory requirement on maximum roll angle. For reference, the A320 has a maximum commandable roll angle of 67 deg in Normal Law, while the A220 has a limit of 80 deg in Normal Mode. The autopilot disconnect bank angles would be much lower than these.

Wow, so informative! Thank you a lot for the links as well :)


text:
What is the amount of lift produced by friction?
As Mr. John D. Anderson states, the aerodynamic forces on a body are due to only two sources: pressure distribution over the body and shear stress distribution.
Shear stress is acting tangential to the surface, so to some amount, friction is also contributing to the lift of a body, not only to drag. But what I most of the time see, is that one is looking at the pressure distribution and integrating this over the surface to get the resulting force.
Do we neglect the part of friction lift because it is so little? But for drag we account for it?

You may add a link to the state of J.Anderson. Moreover, here are some related questions on this website and other resources to help you understand lift generation.

Welcome to Aviation! Please take the [tour] and read through the [help] to get a better idea of how StackExchange sites work so you can get the most out of them.

First, let me illustrate how I understand your question. Please comment accordingly if I got you wrong.
Below you see the friction drag computed by XFOIL for an airfoil at 3° angle of attack.

Friction drag over chord for an E502mod airfoil at 3° AoA. Blue: Top surface, Red: Bottom surface. Source: XFOIL 6.97.
And here is a plot of the pressure distribution at that point:

Where the longest arrow pointing at the airfoil contour points to is the stagnation point. So the large blue peak in the first plot is exactly in the region of the nose where its curvature is strongest and the surface is mostly vertical. Integrating all the friction drag over the height of the airfoil should result in a small upwards component from that high local friction around the nose. Lift, from friction, in other words.
Did I understand that correctly?
I've never seen that component of lift being mentioned separately, and even XFOIL does not include it in its calculations (just checked the FORTRAN source I have lying around). You assume correctly that this component is indeed negligibly small, it is about two orders of magnitude smaller than the pressure forces.

When airfoil is at a non-zero AOA, more shear forces will translate into lift component. Doesn't xfoil compute far-field lift and drag instead of surface integration?

@m2as3registeredservicesohmone: You are right. In XFOIL.f, subroutine CLCALC, the lift coefficient is summed up in the line CL = CL + DX* AG (plop over N panels). No additional summand using DY, so tangential forces are neglected. Since they are two magnitudes lower than pressure, this makes sense.

Let's assume that all of the shear stresses have been converted to lift. Shear stresses manifest in the form of skin friction drag which, for a fully turbulent boundary layer (producing more shear stresses than a laminar one) over a flat plate, has an approximate solution given by (Ref. Anderson, Fundamentals of Aerodynamics):
$$C_f=\frac{0.074}{Re_c^{1/5}}$$
Let's assume a Reynolds number ($Re_c$) of 0.1 million and 2 sides, this gives a drag coefficient of 0.015. If you assume a lift slope of $2\pi$, this translates to an error on attack of attack of only 0.14 deg, even if all the shear stresses have been converted to lift. Needless to say, shear stress is a negligible error component for lift prediction.


text:
In which direction does air flow over a wing as observed from ground?
A wing flies to the left in the air (no wind). Particles A and B moves to the right in relation to wing.

In which direction do particles A and B moves in relation to the ground?
What is velocity of particles in relation to the ground?
Don't forget, air is at rest (no wind) and the wing is moving, so why does particle C not move to the particle A, because the net pressure gradient is to the left and air always travels from high to low pressure?

(i think when observed from ground :
particle A moves up and left
particle B moves down and left
particle C moves down and left
and when wing pass all particles will move down and left)

Related:[https://physics.stackexchange.com/questions/157038/do-particles-always-flow-from-high-to-low-pressure ]

Instead of particle, you should write "dust particle" or any other suited formulation as air molecules move in all direction whereas dust particle average air molecule movements around them. It would remove ambiguity.

You need to clarify your frame of reference.  "From the ground" you would only see the perspective in your diagram if you were on a mountain top and an aircraft flew by at your elevation.

@Rotor A is the one to focus on. It gets pushed up, and the wing runs past it before the lower pressure between it and the wing can pull it back down.  In the process of trying to fill the vacuum, A gets pulled down and the wing gets pulled up.  C is A a fraction of a second later.  The process is constantly repeated as the wing hits "new" air, at the expense of drag.

The wing velocity arrow is greater than your pressure gradient return arrow.  At too high an AOA, the wing cannot "run away", and higher pressure indeed "catches up", breaking the lower pressure "bubble" over the wing.  You actually see these as "reverse flow" arrows in many diagrams of stall towards the rear of the wing.  Yes, they are now moving "forward" faster than the wing.

particle A moves up and left

No, up and right

particle B moves down and left

Yes

particle C moves down and left

Yes
The low pressure region first pulls in the particle A, so it initially moves in the opposite direction of the wing, and then the adverse gradient over the rear part of the wing will gradually accelerate it so it ends up moving a little in the direction of the aircraft. It also ends up moving down much faster than forward, which is how the lift can be much more than the drag.
On highly cambered wings the pressure may be higher than ambient everywhere on the underside, but most wings are not cambered that much and there is some reduction of pressure under them as well, so even the particles moving under the wing accelerate a bit to the right, opposite of the wing, and only then change to moving left along the flight direction.

is velocity of A when first accelarate to the right,same if we meassure from wing or ground refernce frame?

@ROTOR, you asked about when observed from the ground, so I am saying what it is from the ground. From the point of view of the wing, all the air is moving to the right fast. But around the suction peak it is moving faster than free stream, so it's moving right even viewed from the ground (where the free stream is stationary).

@ROTOR, of course accelerations are the same in both reference frames, because we are considering wing in steady flight that is not accelerating relative to the ground.

if wing flying at 1000km/h and A=1100km/h looking from wing,then A=100km/h looking from ground?

@ROTOR, yes, just watch out for directions—when flying 1000 km/h LEFT, and A moves 1100 km/h RIGHT relative to wing, then A moves 100 km/h RIGHT relative to ground, yes. It is vector addition.

Hi Jan are you also aeronautical engineer?

@ROTOR, no, I am not. I just know some physics.

The circulation theory of lift shows that the flow over a lifting airfoil comprises a steady flow against the direction of travel, superimposed on a circulation of air around the airfoil. It is this circulation which defines the lift, and is in turn generated by the pressure gradients (The pressure gradient you show is far from the most significant one, as most of the action takes place near the leading edge).
Take away the steady flow as you have done, and you are left just with the circulation. The circulation flows up over the leading edge, back over the upper surface, down behind the trailing edge and forwards again underneath. You will see A, B and C moving accordingly. For example A has probably already completed its small forward motion (if any) and much of its upward motion, and is well into accelerating backwards. C is just slowing down, possibly ready to turn down, while B is moving forwards and possibly accelerating.
Of course a given particle does not follow the full circle, you can think loosely of a circulatory loop as a string of particles all moving together (although as stated it is a flow component and the particles are also transiting across the loop).
The flow at the front is fairly well confined, the further back you go the more diffuse it becomes, hence the trailing downwash reaches a great deal further than the upwash at the leading edge.
A similar circular motion is sometimes seen when an object floating on the surface of water is subject to waves passing by.

"Circulation" of a wing is probably more like a low pressure system, with the front sweeping behind it, than a hurricane because of the forward movement of the wing.  But new air constantly feeds in from in front, likely splitting at the stagnation point.  The flow off the bottom, at proper AOA, seems to help keep pressure low at top rear wing.  This is what breaks down at stall.

Forward.
A wing is pushing the air out of its way. It pushes the air in the direction it moves itself.
Same way if you stir water in a cup with a teaspoon, the water will move in the direction you move the spoon. It will move slower than the spoon so with relation to the spoon will appear moving backwards.
Or, another comparison: if a locomotive is pushing rail cars "out of its way", they obviously move the direction the locomotive moves, with relation to the ground. If a bulldozer is pushing a pile of sand, the sand is moving the direction bulldozer does, even if some spills into sides.
As the wing is also a wedge, some air will also move up and down is it makes its way through it.

It's not that easy, and it's not that easy for cars either.

Never seen cars moving the opposite direction than locomotive, however.

True… It's because it's actually a bad analogy.

This is a good thought to consider the wing actually strikes the air in real flight, whereas in a wind tunnel it is the opposite, but the resultant flow patterns are the same.
From the ground, particle A is pushed up and forward, B pushed down and forward, but in that time the wing moves father forward, so relative to the wing, "flow" is backwards.
A moving airfoil at positive AOA can be considered a "pump", creating a "circulation" and "downwash" relative to the wing.  Therefor, at any Time 0 to Time X, particle A will be farther behind the wing than particle B, and particle C behind and lower than both from downwash any way you look at at.
Do Time 0 to Time X for A, B, C, and the wing.  You will find point of reference will not matter.  Their relative positions will be the same at Time X, allowing wind tunnel designers to breathe a sigh of relief.
In your diagram, higher pressure (and slower "flow") should be underneath the wing.
The situation you show is what happens when the wing is at too high an Angle of Attack and higher pressure "leaks" over to the top.  This also happens at wing tips and is "bad", causing loss of lift and more drag.  When this happens at the trailing edge, it is called a "stall".

situation on my picture is allways happening on wing,because pressure on leading edge is allways lower then pressure on part of wing close to trailing edge..but velocity of A,B,C are slower when we look from ground than we look from wing?

@Rotor from the ground the velocities are W - A, W - B, W - C, from the wing they are - A, -B, - C.  From the ground the forward motion is W > B > C > A.  From the wing the relative rearward motion is A > C > B > W.  No need to confuse yourself, just use the wing frame of reference, and see the "circulation" towards the "wake" of the wing.  lowest pressure is above and behind the wing, exactly where the drag vector is.

So, please move low pressure further back, and high pressure underneath the wing.


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How do you determine VMCG, if its yawing moment by the inoperative engine is only be corrected by the rudder?
The requirement of VMCG is:
VMCG, the minimum control speed on the ground, is the calibrated airspeed during the takeoff run at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane using the rudder control alone (without the use of nosewheel steering), and the lateral control to the extent of keeping the wings level. In the determination of VMCG, assuming that the path of the airplane accelerating with all engines operating is along the centerline of the runway, its path from the point at which the critical engine is made inoperative to the point at which recovery to a direction parallel to the centerline is completed may not deviate more than 30 feet laterally from the centerline at any point.
How do you determine, this speed by preliminary design? Can it be said, that the centrifugal force is the same as the delta of the engines inoperative? So the Centripetal force is by the rudder if we neglect the tire forces?

In preliminary design it should be the other way around: you have the value of vmcg as requested for example by some regulations and you design the rudder accordingly.

Not sure that centrifugal & centripetal forces are really what's at work... you have a force on a moment arm from the running asymetric engine (no longer balanced by the now-dead engine), and you have a force & moment arm from the rudder, and you want those to be at least in balance (or slightly more provers yaw available from the rudder to return to a straight-ahead track).


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1959 C172 N7393T is on AviationDatabase, can someone post this please?
A user named Michael Matt asked about his grandfather's plane:
"I'm trying to find a 1959 C172 tail number N7393T"
I signed up to tell him I believe I found it on on AviationDatabase, but apparently, I don't have enough credibility to answer. Would someone be so kind as to post the link for him:
https://aviationdb.net/aviationdb/AircraftDetailPage#SUBMIT
His original post is here:
How can I find a deregistered airplane?
He hasn't been active since he asked, but maybe it will notify him.
Thank you.

You may have tried to answer in comments.  Comments require a certain reputation, you build reputation points based on upvotes for questions and answers.  So quickly, before anybody downvotes you on this one, maybe try again, ensuring you post an answer in the answer block?  Good work by the way, if it answers the question you have my upvote. This "question" however, will likely be voted closed. Starting with me...

I’m voting to close this question because it isn't a freestanding question, it is phrased as a request regarding another post.

But if you cannot for some reason, let me know in comments and I will gladly post it as an answer, because I tried and it looks like it works.  Hoping that if you want to continue here you can get credit for the answer...

Hello Hollis Natalie, welcome to aviation.stackexchange.com! You should be able to post this as an answer under the original question. Scroll all the way down  past the other answers and you'll find an editor box to compose the answer. Unfortunately we don't have the tools to convert this question post into an answer to the original question; you will have to repost it there.


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Airplanes crashworthiness and ETSC report
I have recently found this link that shows a report of European Transport Safety Council: https://etsc.eu/increasing-the-survival-rate-in-aircraft-accidents-impact-protection-fire-survivability-and-evacuation/ . This seems to be dated to 1996. What I don't understand is why a lot of recommendations are not yet implemented? Most of them don't look like they would imply a lot of costs or extra training, but they would for sure improve the survivability rate, at least in case of a fire or smoke.
Also I have recently read about the Burnelli airplane wich has a way higher crashworthiness score (but it has some extra air drag which I guess increases the fuel costs), but still I think even a small safety improvement should be above costs or econonics. Why are they not in use today if they provide extra safety and also lower takeoff/landing speeds (when most of the accidents take place)?

You're asking 2 distinct and different questions here: 1) Why haven't recommendations been implemented? 2) Why are extra safety measures not in use? If you'll take the [tour], you'll note that we work on a one-question per post basis. Your best bet would be to separate these into 2 different questions. You'll probably also want to be more explicit in exactly what you're asking because these seem rather broad questions. Also, "a small safety improvement" is often not "above cost/economics" because the cost is high and the improvement is small.

Agreed! I will try to split this into two questions. Regarding the improvement vs cost, in the and it will be propagated to the customer, and I think there is not one person which would not pay an extra premium knowing that it adds an extra safety. But anyways, some of the recommentations seems quite cheap, like for example 3 point seatbelts.

"I think there is not one person which would not pay an extra premium knowing that it adds an extra safety" - I think you're working under an incorrect assumption here. Look at how many people pass up on creature comforts (like a place to put their legs when sitting in a plane seat) in exchange for saving a few dollars on a ticket. If it weren't for consumer's extreme price sensitivity, low-cost carriers wouldn't exist. Also, there can be huge additional maintenance costs for that added "safety" that just doesn't make it economically feasible.

I'm betting if you search through the [tag:safety] questions, you see all sorts of "Why don't they do x to improve safety" questions, 99.9999% of which are answered by "the added cost compared to the added safety isn't viable".


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Calculating True Altitude from ADS-B Data
I am working on a project and need to determine the altitudes of airplanes (trying to determine when they are landing/doing a touch and go).
I have an ADS-B receiver receiving data from the airplanes.
At first I was confused as the reported altitude went below the known altitude of the airport. After further research I found the reported altitude from ADS-B was the uncorrected pressure altitude.
Where I got confused was, how do I correct it to get the true altitude? I know the elevation and barometric pressure at the airport. I saw conflicting answers online of how to calculate this

I believe I have found the correct answer but would like some confirmation:
"True Altitude = Reported Altitude + Airport Altitude - (29.92 - Airport Pressure)*1000"
that airport pressure is the pressure at the airport altitude, not referenced to sea level (as that is the data I have)
Does this seem correct?

Do you need geometric altitude instead of barometric altitude?  It is being supplied by ADS-B as well.

I dont see geometric altitude being received. I can take more of a look and see if its there somewhere I am not logging. I really just want the altitude to match up to the altitude of the airport. It can cause confusion among people if the altitude reported is lower than the altitude of the airport

Do you have the QNH of the airport? What kind of ADS-B are we talking about: UAT or 1090ES?

I dont have the QNH, but do have the altimiter reading at the airport, so QNH should be able to be calculated. I am using dump1090 to get the ADS-B signals. I reviewed the fields I am receiving, and there is just one for altitude. I believe the equation I posted above seems to work in my testing

So you have your own receiver which is connected to dump1090? What is it what you are trying to do with the data? Dump1090 is not including all data that is being sent by the aircraft, I may be able to point you to a different solution if I understand what you want to do.

Yes we have our own receiver connected to dump1090. Our measurements are for a lawsuit so I can't share all the details, but we just want to accurately determine where the aircraft are in relation to a sound level meter we have. The lawyers were confused that the aircraft went below ground level so I am working on correcting that to get a more accurate altitude

No, they calculate it there based on temperature as they say you probably wont have barometric pressure at the ground, but I do not have temperature and do have barometric pressure on the ground

See also the second half of the answer to Is there a place where altitude while flying is negative? which deals with ADS-B receivers altitude.


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N-Number to ADS-B mode s code relationship
I just changed my n-Number. The new n-Number was approved on 21 December. I have already put the new n-Number on the plane, and I want to fly with it, but I read that the ADS-B aircraft identification code that must be programmed into the ADS-B transmiter is tied to the n-number.
When I do an FAA n-number lookup on the new number, it already has a octal code assigned to it, different from the one on the lookup page for the old n-number, (even though the change still shows as "Pending" since I am only today mailing back the FORM 8050-64).
Is this octal code displayed on the lookup page the correct code to be programmed into the ADS-B transmitter?  Is there an algorithm or rule to check to verify that this hex code is the right code for my new n-Number?
The new n-Number is N116B, and the hex code is A04296 (or 50041226 in octal)

Codes look the same. Were you comparing the Mode-S (octal) to the hex code, perhaps? Strangely, just submitted a -64 today as well.

FYI, I called the aircraft registration branch to check on when I can fly her, and all you need to do is keep a copy of the -64 you submitted in the plane with you... you don't need to wait for them to mail back the new registration. In fact, the guy was kind enough to email me a PDF of the -64 so I wouldn't have to wait for snail mail copy to arrive.

I waited for the 64, but you don’t have to take a copy to the FSDO for the airworthiness cert, there’s an online portal for that now. Registration (the 64) still gets mailed.

In the United States, the ICAO hex code and the tail number are related algorithmically. The code A00001 (in hex, 50000001 in octal) is given to tail number N1, A00002 to N1A, and so on in alphanumerical order (with letters before numbers) up to ADF7C7 for N99999.
You could iterate through all possible tail numbers, but fortunately there's a tool to do this, so you don't have to. If you enter your tail number you'll see that the hex code A04296 (50041226 in octal) is indeed the correct ICAO code.


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Can a single-bladed rotor with cyclically varying torque emulate a swashplate?
Instead of a swash-plate cyclically varying the pitch of the rotor blade(s), could a similar effect be generated by cyclically varying the thrust of the motor on a fixed-pitch single-blade rotor? The thrust would be at a maximum at one angle of the rotor, and at a minimum at 180 degrees from the first angle. The blade would still have some inertia at minimum thrust, but ideally the thrust from the motor would be a larger factor.

Probably not as you describe.  You would need to vary the speed of the rotor throughout the revolution.  You might need to double or halve the speed for part of a rev -- that much acceleration would take tremendous torque and does not seem practical.
However, there is some research, papers & another, and patents out of U Penn about a 'Pulsed Cyclic' idea.
The rotor blade has a 45-degree hinge such that pitch is coupled to lag.  When the rotor is pulsed (bump in torque), the blade lags, and the blade pitch increases.  Pulsing the blade as it rotates gives them cyclic control.
All of their work that I've seen works with two-bladed rotors.  However, I suspect you could also apply it to a one-bladed rotor if you wanted.

Thanks for the response Rob. That UAV from UPenn was actually what got me thinking about other ways of controlling thrust cyclically. With a small enough rotor (say a 40mm prop), would doubling/halving the speed really be too much torque? The UPenn rotor seems to change speed from 180 to 220 rad/s within one cycle on a relatively large prop.

Lets assume you can get away with a 1/rev speed change -- max speed at some angle and minimum speed 180 degrees later.  The longer you need to hold those max speeds, the greater the acceleration needed.  For now, lets assume you can get away with sinusoidal velocity.  $\omega=3+sin(\theta)$ has this shape and an RMS of just over 3 (3.0822 rad/sec).  Its derivative is $\dot{\omega}=cos(\theta)$.  Which has peaks at +-1 rad/sec^2.  If you know the blade inertia, you could calculate the torque required ignoring aerodynamics.

In practice, I think you would want a more-square wave shape to get good control authority.


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Can passenger airplanes change model?
Can an old airplane be upgraded, for instance changing from A320 to A320neo? Would this change its tail number?
It doesn't seem common at all, but does it ever happen?

I don't know if any modern airlines for which this is possible. The differences between the A320 and the A320neo are more than just the engines. There is, however, a project running now to re-engine the B-52 to create the B-52J, and the DC-3 has received turboprop engines and a fuselage extension to become the Super DC3. There are others

@CatchAsCatchCan: if you expand your comment a bit and add that also avionics can get update, then you've created a nice answer

As @CatchAsCatchCan mentioned. It's more than the engines. I believe the 737 max 8 incidents are a good example that it's more than swapping engines. The new engines didn't fit the plane and required Boeing to use Software tricks and a Angle-of-Attack-Sensor to make the controls flyable. And what happend because the AOA-Sensor and Software weren't fault-free is known.

@VRK - 737 MAX is flyable without any software add-ons. The issue was that in some situations it handled differently than the previous 737. This would have required simulator training for pilots making the transition, which would have been a cost to the airlines purchasing it. To avoid this the MCAS system was installed which made the MAX handle more like the original 737 in these situations, which would make it more appealing to airlines. As you mentioned there were shortcuts and poor decisions in how Boeing implemented MCAS which led to the accidents.

With enough time and money, anything is possible. But it usually has to look economically viable to actually happen.
If you want a more efficient engine, it usually makes much more sense to buy a brand new plane than to spend money modifying one that already has thousands of hours and cycles on it. There are usually more changes than just new engines as well. Not only are you going to pay for all the work to make the conversion, the conversion will also have to be certified, which is not a fast or cheap process. Airbus already did all the work certifying a plane with the new engine so it makes more sense to just buy that one.
One notable exception is the DC-8, which was upgraded from the JT3D to the CFM56. The model had ended production so airlines couldn't just buy a new one. In addition to the fuel savings (21%, compared to about 15% on the A320 NEO), the noise reduction was a major driver. New regulations required all aircraft the be below a certain noise level that the turbojets and low-bypass turbofans did not meet. This meant the cost of not upgrading wasn't just extra fuel cost, but scrapping the airplanes early. Even when regulations were later relaxed, the alternative was installing hush kits that while being cheaper would also reduce performance. This resulted in 110 of the eligible 262 Super 60 series planes being converted to Super 70s with the new CFM56 engines, a rate of 42%.
The main case where engine upgrades might make sense is with military aircraft. These fleets are much smaller than commercial ones and fly much less, meaning they have much more useful life left even after decades of service and the cost of developing a new airplane is spread across much fewer aircraft. They also have different certification standards. This has resulted in several aircraft types getting upgraded engines:

The KC-135 was upgraded from the J57 turbojets to TF33 turbofans and then later CFM56 turbofans.
The C-130H is being upgraded with new avionics, upgraded engines, and new propellers
The B-52 will upgraded from the TF33 to the F130 (BR700).

And it's not just engines - sometimes major structural work is done to keep military aircraft flying:

The A-10 was fitted with new wings.
The C-5 was upgraded from the TF39 to the F138 (CF6) as well as having major airframe work done.

On a somewhat related note, aircraft like the A320 are offered with multiple options for engine types. In the case of the A320 NEO, customers can choose either the CFM LEAP or Pratt & Whitney PW1000G engines. But once the aircraft is built, even though it is certified with both engines, the configurations are different enough that an aircraft can't be changed to use a different engine type. The 787 is somewhat unique in having a common interface that allows changing between the Rolls-Royce Trent 1000 and GE GEnx-1B engines, but it's unknown if any operator has ever taken advantage of this feature.
The closest thing to engine upgrades in the airliner market is a newer version of the same major engine type. For instance, the CFM56 engines being delivered on the last A320s before they were replaced by the NEO are more efficient than the ones delivered on the first A320s. Swapping for a newer version of the same major engine type is generally possible as the interface remains the same.

Let's look at it from the perspective of something more people are familiar with, cars.
Can you turn a 1985 BMW 320 into a 2015 BMW 320. Same generational difference. The answer is clearly no. You can retrofit a lot of the parts, but it wouldn't turn one into the other. And it's the same with aircraft. Sure, you can upgrade the avionics, put in a new interior, put in some new engines, but you still have the same old airframe structure.
And yes, that is done at times, generating some sort of hybrid that is a bit of both yet neither. The European program to upgrade their F-16A Block 15 aircraft to MLU configuration is a prime example. The old airframes were upgraded with (most of) the avionics and some other systems of the F-16C Block 50. But that didn't make them F-16Cs as the airframe differences weren't incorporated. The main spars and skin for example were not touched (doing that would be useless, it'd end up replacing every single part and effectively building F-16Cs from scratch at far greater cost (and the MLU program already cost more than just buying new F-16Cs instead! The only reason it was even considered was political idiocy where new aircraft weren't allowed for by budgets but "upgrades" were even if those upgrades cost more than new aircraft. I've seen that first hand multiple times with government agencies when working for them as a contractor).

Normally (with the few exceptions already listed in the other answers) a new iteration of the same airplane encompasses more than just maquillage modifications rather under the skin changes that cannot be simply purchased afterward as an upgrade kit. For example the A320 NEO hasn't got only two more modern engines and a different wingtip in respect to the CEO version but also a major structural and aerodynamical redesign of the wing itself plus other improvements in the cabin.
Anyway if we don't just focus on airplane and take into consideration helicopters as well then the answer is yes. A recent example would be the Airbus H145 whose "old" 4-bladed D2 version can be updated to the new 5-bladed D3 version via an upgrade kit.


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Could an air-breathing electric propulsion (ABEP) or other form of ion propelled aircraft fly on Mars?
I'm currently in a class for aircraft propulsion and I became interested in Ion propulsion. It seems there hasn't been many developments for a few years as far as viable aircraft utilizing the technology. To be clear, I'm thinking strictly of a small UAV type aircraft.
From what I understand the thrust produced by various ion propulsion systems is very low and that's the reason they don't work very well on Earth. However, after digging into it a bit I got to wondering if it could be modified to work in the Martian Atmosphere?
To take it further, could an ABEP engine that utilizes CO2 be fitted to work in the Atmosphere? I saw a design for a propeller UAV to fly on Mars, the MAGGIE aircraft, and if the design of the aircraft is there, could the propulsion be changed?

How is "electronic" propulsion also "air breathing"? Because it spins a propeller? Or needs air to generate the electricity? Or something else?

There's a plan to test a spacecraft propulsion system that uses gases gathered from the upper atmosphere as propellant with a solar powered engine to continually re-boost a satellite. The question is could a similar propulsion system work for a Mars aircraft. My immediate reaction is no, I can't see enough thrust being produced to offset drag, but I don't have the means to put that into numbers.

@RalphJ They are air-breathing because the system intakes air as the craft flies and that air is ionized and propelled out the back to generate thrust. Like a ramjet engine, just electric instead of using conventional propellant.

@GdD Are you referring to the ESAs project or something different? If you have a link id love to check it out.

ESA has been looking at this for awhile, now DARPA is in on it too @thewanderingsophist. https://www.theregister.com/2024/02/29/satellite_air_propulsion/

Possibly However the martian atmosphere is absurdly thin, 80x less dense than Earth.
The Martian helicopter "Ingenuity" required larger rotor surface area, and had to spin At FAR higher rpm.
ABEP uses upper atmospheric gases as a propulsion fluid medium. Adopting a design to use martian atmosphere is tricky, as the atmosphere at high altitudes is already.... thin.

"uses upper atmospheric gases as a propulsion fluid medium." I am not sure how accurate it is but I see numbers about the Martian atmosphere being similar to Earths atmosphere somewhere around 35km. Which aircraft have been developed to fly at such an altitude? Also, im assuming they built off of ingenuity to develop, https://www.nasa.gov/general/mars-aerial-and-ground-global-intelligent-explorer/  that. Im just curious if propeller is the only viable solution.

ABEP is still a new concept and the viability of collecting fuel to then produce net thrust would be very low. Supplemental fuel source for a single use case only (i.e. hanging out in the upper atmosphere). Also electron propulsion motors have burn times in the order of months. It would be very hard to do this unless you're travelling a straight'ish line in a vacuum.

Unlikely. The gravity on Mars is only less than Earth's gravity by about a factor of 3. If ion propulsion were practicable on Mars it should at least be possible on Earth as a proof of concept.
A spacecraft is a different story. Since spacecraft don't have to constantly fight against gravity it's possible to do a lot with very small amounts of thrust integrated over long periods of time.